1. Field of the Invention
The present invention relates to methods of making and using an apparatus for providing multi-touch sensing capability using an LCD screen without an extra touch screen layer.
2. Background of the Invention
Liquid crystal displays, known as “LCDs”, are used to create display screens and are widely used on a whole host of various electronic devices, including digital televisions, computer screens, mobile phone screens, and the like.
FIG. 1 illustrates an overview block diagram of a conventional LCD assembly 100 that does not include touch screen or TS capability. As illustrated, the LCD module 100 inputs graphics data 102 that correspond to the color of the pixels to be displayed on the LCD panel 140. The LCD module 100 also inputs DC power along line 101.
With respect to power, the low voltage DC power is typically input to a DC/DC converter of some type to provide higher voltage power to the various internal circuits, i.e. VGH and VGL to the gate driver circuits 150 and VDH and VDL to the source driver circuits 170 as illustrated. The input DC power is also directed to the display controller 130 and to an inverter circuit 120 that powers the backlight lamp 121 of the LCD module 100.
The display controller 130 processes the graphics data signals 102, outputs the timing and control signals to the gate driver integrated circuits 150 and the corresponding timing and pixel color information to the source driver integrated circuits 170.
One gate driver IC 150 is depicted in FIG. 2 and depending on the size and resolution of the LCD panel 140, multiple gate driver IC's can be used to match the panel's vertical resolution. A counter based decoder 152 sends out a single logic 1 signal to each high-voltage buffer 153 sequentially, which in turn drives a high-level voltage (VGH) into the corresponding row line 141 of the LCD panel 140. At the end of the clock period, the logic 1 signal is returned to logic 0 and the row line 141 voltage returns to a low-level voltage (VGL).
One source driver IC 170 is depicted in FIG. 3 and depending on the size and resolution of the LCD panel 140, multiple source driver IC's can be used to match the panel's horizontal resolution. An interface decoder 172 decodes the source driver interface signals 171 into multiple digital words, which represent the intensity of the primary colors of the pixels, and into timing information. These digital words are sent to the correct digital-to-analog converters 173, which output source (column) signals 174 via each of column lines 142 in the LCD panel 140. Source signals 174 are analog voltages between VDH and VDL. A common voltage, Vcom 149, is generated in the source driver IC 170 and is used to bias the common electrode 147 in FIG. 4(b). If Vcom 149 is 0V, then VDH is a positive voltage and VDL is a negative voltage.
FIG. 4(a) illustrates a simplified circuit view of a portion of the conventional LCD panel 140 that does not include touch capability. As shown, there exist the row lines 141, shown in this portion view as rows 141-1, 141-2 and 141-3, as well as column lines 142, shown in this portion view as columns 142-1R, 142-1G and 142-1B, with the RGB standing for red, green, blue respectively. Significant components included within each pixel location (corresponding to the intersection of a row line 141 and a column line 142) include a thin film transistor 143 (TFT), a storage capacitor 144. Other components, well known to one of ordinary skill in the art, are not included for description herein.
FIG. 4(b) illustrates an example of various layers that are used to fabricate an LCD panel 140. As shown, the LCD panel 140 includes a color filter substrate 146, a common electrode 147, and a thin film transistor substrate 148 that contains the plurality of row lines 141 and the plurality of column lines 142. The intersection of each of the row lines 141 and the column lines 142 corresponds to the corner of a pixel, thereby forming a plurality of pixels in a matrix. Each pixel includes one thin film transistor 143 which is coupled to one of the row lines 141 at its gate electrode, one of the column lines 142 at its source (drain), and to the pixel electrode 145 of the storage capacitor 144 at its drain (source). Other layers, well known, are also included though not necessary for description herein.
The operation of a LCD panel is similar to that of a sequentially accessed memory array. All TFT's 143 connected to one row line 141 are first turned on. Source signals 174 on the column lines 142 are transferred into the corresponding storage capacitors 144. After the transfer is competed, the TFT's connected to that row line 141 are then turned off by the gate signal 154. The display controller 130 then proceeds to program the next row until the entire panel is refreshed. The voltages on all storage capacitors are typically refreshed at 60 times per second, or at a sufficiently fast rate in order to allow the human eye to perceive a particular color though the blending of RGB at adjacent pixel locations corresponding to the intensity of the RGB components for those particular column line signals 142.
Various different methodologies are known and used in the conventional LCD module 100 to turn on the various pixel locations in a manner that maintains a perception of continuity, and also is energy efficient.
It is also known to add a touch screen capability to an LCD, thereby allowing for the screen to provide the function of displaying a variety of different visual images, as well as allowing for the same screen to provide the function of detecting a location on the screen that has been touched. A touch function can then allow a whole host of different functions, from pressing a button, drawing a line, to using a finger or pointing device as a cursor.
In the LCD's that have a touch screen, however, the manner in which both capabilities are provided is to have the certain layers (i.e. those that are used to make the LCD screen functionality) used only for generation of graphic images and to have different additional layers used to obtain the touch screen functionality. The major different types of touch screen technologies include touch sensing using a resistive network, a capacitive network, a current flow sensing circuit, a surface acoustic wave detection circuit, a near field imaging detection circuit, an infrared light detection circuit and a strain gauge detection circuit. In all of these implementations, there is an additional layer or layers used for touch sensing, which layer or layers is not used at all for the LCD display.
Advances in the capabilities of touch screen display panels have continued to occur, such that they are becoming widely used. Nevertheless, due to the additional layer or layers needed for touch screen functionality, conventional touch screens are necessarily thicker then a correspondingly similar conventional LCD panel that does not include touch functionality, and, due to the extra layer, lighting efficiency for the LCD is reduced. Furthermore, with the additional layer or layers come extra costs.